The present invention relates generally to control circuits for transformer relays and more particularly to circuits which control the transformer relay upon energization of the primary winding or the secondary winding of the transformer relay.
Transformer relays of the type contemplated to be controlled by the control circuit of the present invention are available in the art. An example is U.S. Pat. No. 3,461,354, Bollmeier, Magnetic Remote Control Switch, issued Aug. 12, 1969, which describes a dual stable state magnetically latchable transformer relay having a primary winding and a secondary winding with the stable state of the transformer relay being determined by the unidirectional flow of current in the secondary winding above a predetermined threshold. The control system for the transformer relay is a rectifier coupled in series with a double pole, double throw momentary action switch which allows the rectifier to be momentarily coupled in either direction across the secondary winding of the transformer relay. Another transformer relay with which the control circuit of the present invention may be utilized is illustrated in U.S. Pat. No. 4,321,652, Baker et al., Low Voltage Transformer Relay, issued Mar. 23, 1982. Baker et al. also discloses a dual stable state magnetically latchable transformer relay having a primary winding and a secondary winding with the direction of a unidirectional flow of current in the secondary winding controlling the state of the transformer relay. The control system disclosed in Baker et al is a single pole, double throw momentary action switch coupled with a pair of diodes, one in each direction, to allow a unidirectional current flow in the secondary winding of the transformer relay in either direction. The transformer relays in both Bollmeier and Baker et al. are magnetically latched to either of two stable states. The control of the state of the transformer relay is provided by the unidirectional flow of current in the secondary winding above a predetermined threshold. A momentary flow in one direction will control the transformer relay to an "on" state (closing a load switch) and a momentary flow of current in the other direction will cause the transformer relay to be controlled to an "off" state (opening a load switch).
A control system for a transformer relay as described in Bollmeier and Baker et al. is described in U.S. Pat. No. 4,338,649, Mosier, A System for Remotely Controlling A Load, issued July 6, 1982. The control systems described in Mosier provide control of a single transformer relay from a plurality of switches or controls.
Another control circuit for a transformer relay is disclosed in U.S. Pat. No. 4,384,314, Doty et al., Control System For Plural Transformer Relays, issued May 17, 1983. The control system in Doty et al. provides electrical isolation for a plurality of transformer relays.
In certain situations it may be necessary to automatically control the transformer relay to a particular predetermined state. For example, if the power source supplying the primary winding of the transformer relay fails or is disconnected, upon reinstatment of that power source it may be desirable or necessary to shut down certain electrical equipment. This may be the case, for example, where the transformer relay controls electrical motors driving air conditioning compressors. Further, if the power source connected to the primary winding of the transformer relay momentarily fails, it may be desirable to set an indicator to indicate this condition. With certain loads connected it may be desirable to check the proper functioning of the equipment following a momentary loss in power.